1. Field of the Invention
The present invention relates to an electrochemical cell, a system and a process for producing carbonyl halide from halogen produced by the electrochemical conversion of anhydrous hydrogen halide. In this conversion, essentially anhydrous hydrogen halide, which is molecular in form, is oxidized to produce protons and halogen. The halogen reacts with carbon monoxide to produce a carbonyl halide, such as carbonyl chloride (phosgene) or carbonyl fluoride.
2. Description of the Related Art
Phosgene is currently commercially produced by passing carbon monoxide and chlorine over activated carbon in a phosgene generator. This reaction must be carried out in the presence of a catalyst. The chlorine is usually produced from conventional chloralkali electrolysis or HCl electrolysis, which produce wet chlorine gas, or from evaporators in which liquid chlorine is evaporated. Usually, chlorine is fed through a preheater before mixing with carbon monoxide in the phosgene generator in order to avoid introducing liquid chlorine into the phosgene generator. Thus, the production of phosgene from a catalyst involves a multi-step process carried out in multiple pieces of equipment, which contributes to the capital investment and operating costs associated with producing phosgene. In addition, phosgene can be formed at high temperatures from chlorinated hydrocarbons with atmospheric oxygen. However, this reaction can lead to possible health hazards. See Ullmann's Encyclopedia of Industrial Chemistry, Fifth Edition, Volume A 19, pages 411-419.
Phosgene is an important starting compound in the production of intermediates and end products in many branches of large-scale industrial chemistry. For instance, it is used widely in the preparation of isocyanates, which are in turn used in the preparation of polyurethanes and in the manufacture of polycarbonates. It is also used in the synthesis of pharmaceuticals and pesticides.
In addition, phosgene, together with either sodium fluoride or hydrogen fluoride, can be used to make carbonyl fluoride. Carbonyl fluoride is a specialty fluorinating agent. It is used to make vinyl ethers and is an intermediate for other fluoroproducts. It is not used in large quantities because it is expensive to make.
Hydrogen chloride (HCl) or hydrochloric acid is a reaction by-product of many manufacturing processes which use chlorine. For example, chlorine is used to manufacture polyvinyl chloride, isocyanates, and chlorinated hydrocarbons/fluorinated hydrocarbons, with hydrogen chloride as a by-product of these processes. Because supply so exceeds demand, hydrogen chloride or hydrochloric acid often cannot be sold or used, even after careful purification. Shipment over long distances is not economically feasible. Discharge of the chloride ions or the acid into waste water streams is environmentally unsound. Recovery of the chlorine for use in a manufacturing process is the most desirable route for handling the HCl by-product.
Therefore, the need exists for developing a simple, inexpensive method for producing carbonyl halide, and in particular, carbonyl chloride or carbonyl fluoride, as well as for disposing hydrochloric acid. It would be desirable to develop equipment and a process which satisfy both needs at the same time.